Generic Name
DrugBank Accession Number

Almasilate is a buffering antacid that has been used in peptic ulcers and dyspepsia. It is a crystalline polyhydrate of aluminium/magnesium silicate and mediates its buffering activity by binding hydrogen ions within the polymer. However its therapeutic efficacy is not comparable to other approved antacids, as it is no more effective in neutralizing acid and binding bile salts than other conventional antacids 1.

Given that there are generally more widely available conventional antacids that are just as - if not more - effective than almasilate, almasilate products are only available in certain parts of Europe and/or Asia.

Small Molecule
Approved, Experimental
Average: 280.445
Monoisotopic: 279.8718534
Chemical Formula
  • Almasilate
  • Almasilato
  • Almasilatum
  • Magnesium aluminosilicate hydrate



Almasilate is indicated for use as an antacid for the neutralization of excess stomach acid 8. It is subsequently also used for the symptomatic treatment of diseases where it is necessary to neutralize acid in the stomach, for example, for treating stomach and duodenal ulcers or heartburn and stomach conditions caused by excess stomach acid 8.

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Associated Conditions
Indication TypeIndicationCombined Product DetailsApproval LevelAge GroupPatient CharacteristicsDose Form
Symptomatic treatment ofAcid indigestion••• •••••
Symptomatic treatment ofHeartburn••• •••••
Symptomatic treatment ofSour stomach••• •••••
Symptomatic treatment ofUpset stomach••• •••••
Contraindications & Blackbox Warnings
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Various non-prescription antacid products are available to the general public to purchase and use as a treatment for relieving the occasional, limited, and non-severe sensation of heartburn (or acid indigestion) that may frequently be associated with stomach indigestion (or dyspepsia) or gastroesophageal reflux disease (when stomach contents may rise back up into the esophagus and cause a taste of acid in the back of the mouth, among other symptoms) 3.

Subsequently, when excessive amounts of acids are produced in the stomach (either owing to indigestion or acid reflux, for example), the natural mucous barrier protecting the lining of the stomach can be damaged 3. Antacids like almasilate consequently contain alkaline ions that chemically neutralize such stomach gastric acids, providing relief to heartburn, relieving pain, and reducing damage in the area 3.

Mechanism of action

Almasilate is a crystalline polyhydrate of aluminum/magnesium silicate and mediates its buffering activity by binding hydrogen ions within the polymer 5. Specifically, the aluminosilicate minerals dissolve, and in doing so consume acidic hydrogen ions and release moieties like H4SiO4, Al3+, and other cations, including the magnesium associated with the compound 5. Almasilate consequently contributes to the overall acid-neutralization by consuming acid hydrogen ion in this way 5. Additionally, aluminum and other metals released from the original compound may also accumulate into secondary aluminum and magnesium based antacid like products that can act as secondary pH buffers 5.


In regards to aluminum-containing antacids like the aluminum-magnesium complex almasilate, it is reported that the bioavailability of ingested aluminum from such antacids is only between 0.01-1% 5. Additionally, while the optimal absorption of magnesium appears to be in the small intestine and particularly in the ileum and jejunum, with some absorption in the colon, it is believed that the transfer of magnesium from blood to extravascular space is quick and efficient 2.

Volume of distribution

The distribution of aluminum can occur in the bones, lungs, spleen, liver, kidney, nervous tissues, muscles, the blood itself, and the heart 6. The highest levels of aluminum in mammalian tissues are found in the skeleton, lungs, kidneys, spleen, thyroid, and parathyroid glands 7.

Conversely, approximately half of the total magnesium in the body is distributed intracellularly in soft tissue and the other half is present in the bones 2. Less than 1% of the total magnesium content is present in the blood 2. In pregnant women, apparent volumes of distribution were evidently observed to range from 0.250 to 0.442 L/kg 2.

Protein binding

Once present in the bloodstream, 60% of aluminum is bound to transferrin proteins, 34% is bound to albumin protein, and the remainder is bound to citrate in the normal human blood serum 7. Furthermore, 33% of serum magnesium is bound to protein, where approximately 75% of the protein bound fraction of magnesium is bound to albumin and the remaining 25% to globulins 2.


Once aluminum has entered the body, the mechanism by which it is metabolized is still not fully known 6. Conversely, magnesium balance in the body is predominantly managed via a balance between intestinal absorption, exchange with bone, and renal excretion 4.

Route of elimination

The routes of excretion of aluminum in the body are mainly from the kidneys, which account for 95% of the elimination 6. Magnesium is largely excreted in the urine 4.


Readily accessible data regarding the half-life of almasilate is not available.


Readily accessible data regarding the clearance of almasilate is not available.

Adverse Effects
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Readily accessible data regarding the toxicity of almasilate is not available.

Not Available
Pharmacogenomic Effects/ADRs
Not Available


Drug Interactions
This information should not be interpreted without the help of a healthcare provider. If you believe you are experiencing an interaction, contact a healthcare provider immediately. The absence of an interaction does not necessarily mean no interactions exist.
AbacavirAbacavir may decrease the excretion rate of Almasilate which could result in a higher serum level.
AceclofenacAceclofenac may decrease the excretion rate of Almasilate which could result in a higher serum level.
AcemetacinAcemetacin may decrease the excretion rate of Almasilate which could result in a higher serum level.
AcetaminophenAlmasilate can cause a decrease in the absorption of Acetaminophen resulting in a reduced serum concentration and potentially a decrease in efficacy.
AcetazolamideAcetazolamide may increase the excretion rate of Almasilate which could result in a lower serum level and potentially a reduction in efficacy.
Food Interactions
  • Take after a meal.
  • Take with a full glass of water.


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International/Other Brands
Mixture Products
NameIngredientsDosageRouteLabellerMarketing StartMarketing EndRegionImage
Ohtas Isan AntacidAlmasilate (83.3 mg/1) + Calcium carbonate (133.3 mg/1) + Sodium bicarbonate (133.3 mg/1)TabletOralOhta's Isan Co., Ltd2012-12-01Not applicableUS flag
Ohtas Isan AntacidAlmasilate (125 mg/1) + Calcium carbonate (200 mg/1) + Sodium bicarbonate (200 mg/1)TabletOralOhta's Isan Co., Ltd2000-11-16Not applicableUS flag


ATC Codes
A02AD05 — Almasilate
Drug Categories
Chemical TaxonomyProvided by Classyfire
This compound belongs to the class of inorganic compounds known as post-transition metal silicates. These are inorganic compounds in which the largest oxoanion is silicate, and in which the heaviest atom not in an oxoanion is a post-transition metal.
Inorganic compounds
Super Class
Mixed metal/non-metal compounds
Post-transition metal oxoanionic compounds
Sub Class
Post-transition metal silicates
Direct Parent
Post-transition metal silicates
Alternative Parents
Miscellaneous silicates / Post-transition metal salts / Metalloid salts / Inorganic salts / Inorganic oxides
Inorganic metalloid salt / Inorganic oxide / Inorganic post-transition metal salt / Inorganic salt / Post-transition metal silicate / Silicate
Molecular Framework
Not Available
External Descriptors
Not Available
Affected organisms
  • Humans and other mammals

Chemical Identifiers

CAS number
InChI Key
dialuminium(3+) ion magnesium(2+) ion hydrate disilicate


General References
  1. Authors unspecified: Magaldrate and almasilate--complex buffering antacids. Drug Ther Bull. 1985 May 20;23(10):39-40. [Article]
  2. Ranade VV, Somberg JC: Bioavailability and pharmacokinetics of magnesium after administration of magnesium salts to humans. Am J Ther. 2001 Sep-Oct;8(5):345-57. [Article]
  3. Ford AC, Moayyedi P: Dyspepsia. Curr Opin Gastroenterol. 2013 Nov;29(6):662-8. doi: 10.1097/MOG.0b013e328365d45d. [Article]
  4. Seo JW, Park TJ: Magnesium metabolism. Electrolyte Blood Press. 2008 Dec;6(2):86-95. doi: 10.5049/EBP.2008.6.2.86. Epub 2008 Dec 31. [Article]
  5. ScienceDirect: Aluminosilicate Profile [Link]
  6. University of Ottawa, Interdisciplinary Journal of Health Sciences: Human Health Effects of Dietary Aluminum [File]
  7. Healthy Canadians: Water Aluminum [File]
  8. Package Leaflet: Information for the patient, Megalac Almasilate 1 g /10 mL Suspension [File]
PubChem Compound
PubChem Substance

Clinical Trials

Clinical Trials


Not Available
Not Available
Dosage Forms
Not Available
Not Available


Not Available
Experimental Properties
Not Available
Predicted Properties
pKa (Strongest Acidic)9.82Chemaxon
pKa (Strongest Basic)-4.8Chemaxon
Physiological Charge0Chemaxon
Hydrogen Acceptor Count4Chemaxon
Hydrogen Donor Count0Chemaxon
Polar Surface Area92.24 Å2Chemaxon
Rotatable Bond Count0Chemaxon
Refractivity5.77 m3·mol-1Chemaxon
Polarizability5.14 Å3Chemaxon
Number of Rings0Chemaxon
Rule of FiveYesChemaxon
Ghose FilterNoChemaxon
Veber's RuleNoChemaxon
MDDR-like RuleNoChemaxon
Predicted ADMET Features
Not Available


Mass Spec (NIST)
Not Available
Not Available
Chromatographic Properties
Collision Cross Sections (CCS)
Not Available

Drug created at June 23, 2017 20:44 / Updated at February 21, 2021 18:54